1. Field of the Invention
Embodiments of the invention generally relate to gravel packing of wells. In particular, the invention relates to methods and apparatuses suitable for injecting gravel slurry at high flow rates within the well bore being packed.
2. Description of the Related Art
Hydrocarbon wells, especially those having horizontal wellbores, typically have sections of wellscreen comprising a perforated inner tube surrounded by a screen portion. The screen blocks the flow of unwanted materials into the wellbore. Despite the wellscreen, some contaminants and other unwanted materials like sand, still enter the production tubing. The contaminants occur naturally and are also formed as part of the drilling process. As production fluids are recovered, the contaminants are also pumped out of the wellbore and retrieved at the surface of the well. By controlling and reducing the amount of contaminants that are pumped up to the surface, the production costs and valuable time associated with operating a hydrocarbon well will likewise be reduced.
One method of reducing the inflow of unwanted contaminants includes gravel packing. Normally, gravel packing involves the placement of gravel in an annular area formed between the screen portion of the wellscreen and the wellbore. In a gravel packing operation, a slurry of liquid, sand and gravel (“slurry”) is pumped down the wellbore where it is redirected into the annular area with a cross-over tool. As the gravel fills the annulus, it becomes tightly packed and acts as an additional filtering layer along with the wellscreen to prevent collapse of the wellbore and to prevent the contaminants from entering the stream of production fluids pumped to the surface. Ideally, the gravel uniformly packs around the entire length of the wellscreen, completely filling the annulus. However, during gravel packing, the slurry may become less viscous due to loss of fluid into the surrounding formations or into the wellscreen. The loss of fluid causes sand bridges to form. Sand bridges create a wall bridging the annulus and interrupting the flow of the slurry, thereby preventing the annulus from completely filling with gravel.
The problem of sand bridges is illustrated in FIG. 1, which is a side view, partially in section of a horizontal wellbore with a wellscreen therein. The wellscreen 30 is positioned in the wellbore 14 adjacent a hydrocarbon bearing formation therearound. An annulus 16 is formed between the wellscreen 30 and the wellbore 14. FIG. 1 illustrates the path of gravel 13 as it is pumped down the production tubing 11 in a slurry and into the annulus 16 through a crossover tool 33.
Also illustrated in FIG. 1 is a formation including an area of highly permeable material 15. The highly permeable area 15 can draw liquid from the slurry, thereby dehydrating the slurry. As the slurry dehydrates in the permeable area 15 of the formation, the remaining solid particles form a sand bridge 20 and prevent further filling of the annulus 16 with gravel. As a result of the sand bridge, particles entering the wellbore from the formation are more likely to enter the production string and travel to the surface of the well. The particles may also travel at a high velocity, and therefore more likely damage and abrade the wellscreen components.
In response to the sand-bridging problem, shunt tubes have been developed creating an alternative path for gravel around a sand bridge. According to this conventional solution, when a slurry of sand encounters a sand bridge, the slurry enters an apparatus and travels in a tube, thereby bypassing the sand bridge to reenter the annulus downstream.
FIG. 2 shows a sectional view of a prior art nozzle assembly 50 disposed on a shunt tube 55. The construction for an exit point from the shunt tube 55 involves drilling a hole 80 in the side of the tube, typically with an angled aspect, in approximate alignment with the slurry flow path 75, to facilitate streamlined flow. The nozzle assembly 50, having a tubular outer jacket 65, and a tubular carbide insert 60, is held in alignment with the drilled hole 80, and the outer jacket is attached to the tube with a weld 70, trapping the carbide insert 60 against the tube 55, in alignment with the drilled hole 80. The nozzle assembly 50 also has an angled aspect, pointing downward and outward, away from the tube 55. Sand slurry exiting the tube 55 through the nozzle 50 is routed through the carbide insert 60, which is resistant to damage from the highly abrasive slurry.
Both the method of constructing the nozzle 50 and the nozzle itself suffer from significant drawbacks. Holding the nozzle assembly 50 in correct alignment while welding is cumbersome. A piece of rod (not shown) must be inserted through the nozzle assembly 50, into the drilled hole 80, to maintain alignment. This requires time, and a certain level of skill and experience. During welding, the nozzle assembly 50 can shift out of exact alignment with the drilled hole in the tube due to either translational or rotational motion. After welding, exact alignment between the nozzle 50 and the drilled hole 80 is not assured. Because the carbide insert 60 actually sits on the surface of the tube 55, the hole 80 in the tube wall is part of the exit flow path 75. Abrasive slurry, passing through the hole, may cut through the relatively soft tube 55 material, and bypass the carbide insert 60 entirely, causing tube failure.
Therefore, there exists a need for an improved nozzle assembly for a shunt tube and a method for attaching the nozzle to the shunt tube.